Convection ovens and dryers that process continuous streams of product are in wide use. In many ovens the product moves horizontally at one or more levels, either carried on parallel moving conveyors or, in the case of textiles or webs, suspended under tension between external drives. A circulating hot air flow is brought in contact with the product for heating or drying. A technically important class of ovens treats polymeric or organic carbon fiber precursors in air to provide thermoplastic properties prior to carbonization.
Ovens for providing oxidative heat treatment to carbon fiber precursor materials such as polyacrylonitrile (PAN) are known in the industry. U.S. Pat. No. 6,776,611 describes an oven in which the heating airflow is circulated around the PAN in tow format and contacts the fiber in a direction perpendicular to the direction of tow travel. U.S. Pat. No. 4,515,561 discloses an oven in which the heating airflow is circulated around the PAN in tow format and contacts the fiber in a direction parallel to the direction of tow travel.